1. Field of the Invention
The present invention relates to an air-to-fuel ratio adjusting system for an internal combustion engine which is operable to adjust the air-to-fuel ratio of gas mixture to be fed to an internal combustion engine to an optimum value depending on the operating condition of the engine, by feeding back an air-to-fuel ratio of gas mixture exhausted to an exhaust pipe for accomplishing the purification of the exhaust gas in the internal combustion system.
2. Description of the Prior Art
A carbureter is generally designed and conditioned to be operable to feed gas mixture of an optimum air-to-fuel ratio under any operating condition of the internal combustion engine. However, when atmospheric temperature and/or atmospheric pressure change, the air-to-fuel ratio of the gas mixture varies, which has brought about a problem of resulting in not only the generation of noxious exhaust gases but also the reduction of the purification ability of a catalyst mounted for purifying the exhaust gas as well as the deterioration of the catalyst itself.
Meanwhile, a system has been proposed in which the air-to-fuel ratio of the gas mixture is detected in terms of the oxygen concentration in the exhaust gas and it is fed back to control the air-to-fuel ratio of the gas mixture to an optimum value. However, since an air-to-fuel ratio detector has poor detecting ability when the temperature of the detector itself is low, the detection of the air-to-fuel ratio at a low temperature has been impossible. For example, during the warm-up period of the internal combustion engine following the start-up of the engine, the temperature of the exhaust gas is too low to conduct the heat to the detector and hence the detection of the air-to-fuel ratio is impossible.